Diesters of aromatic dihydroxy carbonyl compounds and branched chain fatty acids containing a quaternary carbon atom

ABSTRACT

ESTERS OF CERTAIN BRANCH CHAIN FATTY ACIDS CONTAINING A QUATERNARY CARBON ATOM AND CERTAIN DIHYDROXY AROMATIC CARBONYL COMPOUNDS (E.G., BENZOPHENONES, NAPHTHOPHENONES) ARE EMPLOYED AS BASE FLUIDS OR BLENDING STOCK IN LUBRICANTS, LUBRICANTS CONTAINING THESE ESTERS POSSESS SUITABLE VISCOSITY CHARACTERISTICS AND GREATER THERMAL AND OXIDATIVE STABILTIY WHICH ARE OF SPECIAL VALUE IN LUBRICATING ENGINES WHICH ARE SUBJECT TO HIGH TEMPERATURES.

United States Patent 3,632,630 DIESTERS OF AROMATIC DIHYDROXY CAR- BONYL COMPOUNDS AND BRANCHED CHAIN FATTY ACIDS CONTAINING A QUATERNARY CARBON ATOM Tai S. Chao, Homewood, Ill., and Manley Kjonaas, Hammond, Ind., assignors to Atlantic Richfield Company No Drawing. Filed Aug. 17, 1967, Ser. No. 661,237 Int. Cl. C07c 69/28 US. Cl. 260-479 8 Claims ABSTRACT OF THE DISCLOSURE Esters of certain branched chain fatty acids containing a quaternary carbon atom and certain dihydroxy aromatic carbonyl compounds (e.g., benzophenones, naphthophenones) are employed as base fluids or blending stock in lubricants. Lubricants containing these esters possess suitable viscosity characteristics and greater thermal and oxidative stability which are of special value in lubricating engines which are subject to high temperatures.

This invention is concerned with synthetic esters for use as base fluids or blending stock in lubricants. Lubricants composed in whole or in part of synthetic components have been developed in an efiort to obtain superior lubricating compositions. In general, these lubricating compositions are characterized by higher viscosity indexes, lower pour point and greater thermal and oxidative stability than mineral oils of corresponding viscosity. Such properties are of special value in lubricating engines which are subjected to high temperatures, such as combustion turbine engines. Mineral oil lubricants, even those containing added VI improvers, pour point depressors, or other additives are undesirable for use in such engines because of the relatively high volatility, low flash point and poor thermal and oxidative stability of the mineral oils, which also have a tendency to leave deposits which accumulate and interfere with the operation of the engine. Particularly, in high performance jet engines, such as those designed for supersonic transport and other advanced aircraft, and in industrial gas turbines which operate continuously at full power settings, lubricants are required to have high thermal and oxidative stability.

Certain neoalkylpolyol esters of straight chain fatty acids, eg pentaerythritol tetracaproate, which are known as Type II lubricants, have been employed in jet engines but do not possess the thermal and oxidative stability required of the more advanced engine models. On the other hand, esters derived from neoalkylpolyols and branchedchain fatty acids, e.g., pentaerythritol tetrapivalate, although having good oxidative stability, are solids at room temperatures and thus have poor handling, starting and low temperature properties. Polyphenyl ethers, e.g., m,m,m bisphenoxyphenoxybenzene, have pour points above 3540 F. and do not flow and pour at subzero temperatures, as required to achieve their functions, especially during the critical start up time for jet engines.

It has now been found that the esters formed by reacting certain branched chain fatty acids or acid chlorides containing a quaternary carbon atom with certain dihydroxy aromatic carbonyl compounds possess superior properties of thermal and oxidative stability along with suitable viscosity, volatility and low temperature properties and therefore may be employed as either base fluids or blending stocks in lubricants for high performance supersonic aircraft and other appropriate applications. In addition, these esters can be used as base fluid or thickener for high temperature hydraulic fluids, base fluid for high temperature greases and as components for other lubricants which require high thermal and oxidative sta- 3,632,630 Patented Jan. 4, 1972 ice bility. They can also be used as advanced plasticizers for high temperature polymers such as polyvinyl chloride, polyethylene, polyesters, polycarbonates, polyurethanes, polyamides, polyimides, synthetic rubber, etc.

Aromatic dihydroxy carbonyl compounds suitable for forming the esters of this invention may be described by the general formula wherein x and y each equals 0-2, and x+y=24, A and A are aromatic hydrocarbons containing from 6 to 20 carbons, particularly the benzene and naphthalene radicals. Exemplary of compounds suitable in the present invention are: 2,2-dihydroxybenzophenone, 4,4-dihydroxybenzophenone, 2,4 dihydroxybenzophenone, 2,4-dihydroxybenzophenone, 2,2-dihydroxy-4,4'-dimethoxybenzophenone, 2,2'-dihydroxynaphthophenone and 2,2-dihydroxybenzobiphenone. These compounds are generally prepared by reacting the appropriate phenols and aromatic hydroxy acids using condensation agents such as ZnCl and P001 The fatty acid chlorides are prepared by reacting appropriate fatty acids with compounds such as PCl PCl SOCl These fatty acids have the general structure:

where m=0 to 3 and R R and R are alkyl groups having 1 to 4 carbons. Exemplary of these acids are the following: 2,2-dimethylpentanoic acid, 3,3-dimethylpentanoic acid, 4,4-dimethylpentanoic acid, 4,4-dirnethylhexanoic acid, 3,3,4-trimethylpentanoic acid, 4,4,5-trimethylhexanoic acid, 3,3-dimethylbutanoic acid, 2-methyl-2-ethyl-pentanoic acid, 3-methyl-3-ethyl pentanoic acid, 3- methyl-3-ethyl butanoic acid or mixtures of these acids.

The esterification reaction with the dihydroxy carbonyl compounds can be carried out using either the fatty acid directly or using the acid chloride. In the event the fatty acid is reacted directly with the aromatic hydroxy compound a suitable reagent such as trifluoro-acetic anhydride or poly-phosphoric acid can also be employed to combine with the water of reaction. If the acid chloride is employed rather than the acid, the reaction is facilitated by the presence of a compound which will react with the HCl as it is formed. Such HCl acceptors include certain amines which have no hydrogen on the nitrogen atom such as pyridine, dimethyl aniline, and triethylamine and also inorganic bases such as Na CO and CaCO The HCl may also be removed from the reaction mixture by applying suflicient heat and bubbling nitrogen through it. Suitable solvents such as benzene, toluene, xylene, chloroform and ether may be employed to facilitate the reaction and to make stirring easier. The rate of the reaction is increased by the use Of a catalyst such as dimethyl formamide.

The esters produced by this process may be represented generally by the structure:

where m and 11:0-3 and R R R x and y are as previously described.

Typical esters of this type, which are produced by the process of this invention, can have the structure:

e Q 2E A q sm w e w ie fia8\ v: x: E 8 :83 HHHHnHunHHE W.-...-.-:.-.:::::-.-:...-.-..:.-:.:-:::.....Hn.fie. E wmm ommd mam i mam m owmfi l i I I I l i I I I I I woo m 15E B 6 26 5 5. gm 982 282 Z 2 5 m s e m 5 Zsm ea Zm x; sea HMHHHHH W H wmm izwnwsm n ci wv iml 2 E a w Sum H m 3 Q E is is its -HHH---HHHH.--H-..H.H we a .22 mm 2 4 2a w 5 8: 9 H HHHufi H m g e2 a2 a 8 2 2 E 30m E S B 2 m 02w )4 4 6 295 E h on: m 2%. am n ew ewnwm awwewm -osee sfih egea m 682553535 s fi flfi am 2 3 523 52 N E3 e see N such as, for example, 2,2'bis(2,2-dimethylpentanoyloxy) benzophenone or 4,4 bis(2,2 dimethylpentanoyloxy) benzophenone, or can have the structure such as, for example, 2,4-bis (2,2-dimethylpentanoyloxy) benzophenone 0r 2,4 bis (3,3 dimethylpentanoyloxy) benzophenone.

Examples of esterification reactions producing the prodnets of this invention are given below.

ians a EXAMPLE I A mixture of 213 g. (1 mole) of 2,4-dihydroxybenzophenone and 500 g. of toluene was refluxed until no more water was collected in the Dean-Stark trap. Only a few drops of water were obtained. To the stirred solution was added 15 ml. of dimethyl formamide. The mixture was stirred at 88-112 for about 7 hrs. during which 653 g. (4.4 moles) of 2,2-dimethylpentanoyl chloride and 15 ml. of dimethyl formamide were added. After stirring at 112- 6 for about 30 min., the mixture was cooled to room temperature. About ml. of pyridine was added and the mixture was stirred at 60-100" for 6 hrs. The reaction mixture, upon cooling, was washed twice with 1.2 N HCl, three times With 20% NaOH and then twice with water. The washed solution was topped to 175 C. at 1 mm. About 352 g. of clear viscous liquid was obtained.

EXAMPLE II A mixture of 205 g. (0.96 mole) of 4,4-dihydroxybenzophenone and 400 g. of toluene, after removing trace of water by azeotropic distillation, was stirred at 170- 195 F. for '9 hrs., while 15 ml. of dimethylformamide and 315 g. (2.12 mole) of 2,2-dimethylpentanoyl chloride were added slowly. The mixture was then refluxed with 60 ml. of pyridine and worked up in the same manner as Example I, yielding 393 g. of product. The latter solidified upon standing and was recrystallized from methanol.

The esters of this invention have been found to possess improved oxidation resistance over conventional base fluids used in Type II synthetic lubricants. Oxidation resistance is determined by the Oxygen Absorption Test which measures the rate of oxygen absorption in the presence of an inhibitor such as 1% N-phenyl-ot-naphthylamine.

The Oxygen Absorption Test is carried out in the following manner: a 75 gm. sample of the ester containing a standard antioxidant is oxidized at 450 F. with 1 ft. /hr. of oxygen in a tube about 9" long and 1%" in ID. The exit gas passes through a reflux condenser, an entrainment trap and two absorption tubes. The first tube is filled with active charcoal, Drierite and Ascarite to remove organic vapor, water and C0 The gases come out 60 from the first tube then pass through a catalytic oxidation tube filled with CuO, in which CO and hydrocarbons are converted to C0 The exit gas from the oxidation tube then passes through a second absorption tube filled with Drierite and Ascarite and is circulated with a tubing pump back into the sample tube. Thus oxygen is continuously circulated through the system until it is used up by the sample. The decrease in the volume of oxygen in the system which represents the volume of O absorbed is continuously measured by a Stathum gauge and recorded on a Brown recorder. The recorder is so calibrated that the slope of the curve represents the rate of oxygen absorption. During the earlier part of the test the oil is effectively inhibited by the antioxidant and the rate of 0 absorption is usually small. The rate usually stays constant until a time is reached at which the inhibitor is either exhausted or is no longer effective in inhibiting the oxidation. At this point there is generally a fast increase in the rate of oxidation. The time in minutes required for this change of rate to happen is called induction time (T The volume of O absorbed during this period of time is represented by V The test is continued until a total of 2500 ml. of has been absorbed. The time in minutes for this to take place is called total time (T The total volume of O absorbed (V is usually 2500 ml., unless some other (V was used for special reasons.

A conventional base fluid for Type II synthetic lubricants, pentaerythritol tetracaproate, was subjected to the Oxygen Absorption Test along with the esters of this invention. The results are summarized in Table I.

As may be seen, pentaerythritol caproate (col. 6) was found to have an induction time (T of 260 min. and a total time (T,) of 298 min. Compared with this all of the compounds of the present invention (cols. 1-5) experienced no drastic increase in oxidation rate during the test. This is reflected by the total absence of an induction time (T for these compounds. The time required for the compounds tested to absorb 2500 ml. of oxygen, the total time (T,) was -10 times that required by pentaerythritol caproate, ranging in the former case from 1560 min. to 2930 min. as compared with 298 min. for the conventional base fluid.

Further, it may be observed that the compounds of the present invention have greater oxygen tolerance than conventional esters. This means that they suffer much smaller changes in physical properties such as viscosity upon oxidation. For example, in Table I it will be seen that the pentaerythritol caproate experienced a 43.95% change in Kinematic Viscosity at 100 F. (Akv./100) after the relatively short time of 298 min. (T when subjected to the Oxygen Absorption Test. The compounds of this invention undewent similar changes in viscosity, ranging from 32.1% to 59.5% only after the much longer period of from 1560 to 2930 min.

In addition to being used by themselves as base fluids the compounds of this invention may also be blended with other ester type base fluids.

Table -II shows some of the critical properties of mixtures of these esters. The ester chosen is resorcinol dineoheptanoate, although other aliphatic or aromatic esters containing 2 or more ester groups can also be used. It can be seen that a base fluid having a pour point of 45 F. and kv./ 210 of 5.304 c.s. can be obtained by blending 1 part by wt. of 4,4'-bis(2,2 dimethylpentanoyloxy) beuzophenone with 2 parts by wt. of resorcinol dineoheptanoate. With a suitable choice of the esters of this invention and a suitable choice of the other ester component and additives, synthetic lubricants of superior thermal and oxidative stability and adequate physical properties can readily be obtained.

TABLE II.PROPERTIES OF MIXTURES OF ESTERS OF THIS INVENTION WITH OTHER ESTERS It is claimed:

1. Diesters of (a) an aromatic dihydroxy carbonyl compound of the formula 6 wherein x and y each is from 0 to 2, however, x+y is 2, and A and A are aromatic hydrocarbon radicals selected from the group consisting of the benzene and naphthalene radicals, and (b) a branched chain acid having a quaternary carbon atom selected from the group consisting of 2,2-dimethylpentanoic acid, 3,3-dimethylpentanoic acid, 4,4-dimethylpentanoic acid, 4,4-dimethylhexanoic acid, 3,3,4-trimethylpentanoic acid, 4,4,5-trimethylhexanoic acid 3,3-dimethylbutanoic acid, 2-methyl-Z-ethylpentanoic acid, 3-methyl-3-ethylpentanoic acid, 3-methyl-3-ethylbutanoic acid and mixtures thereof.

2. Diesters of (a) an aromatic dihydroxy carbonyl compound of the formula 0 )x 1 2( )y wherein x and y each is from 0 to 2, however x-l-y is 2, and A and A are benzene radicals, and (b) a branched chain acid having a quaternary carbon atom selected from the group consisting of 2,2-dimethylpentanoic acid, 3,3-dimethylpentanoic acid, 4,4-dimethylpentanoic acid, 4,4-dimethylhexanoic acid, 3,3,4-trimethylpentanoic acid, 4,4,5-trimethylhexanoic acid 3,3-dirnethylbutanoic acid, 2-methyl-2-ethylpentanoic acid, 3-methyl-3-ethylpentanoic acid, 3-methyl-3-ethylbutanoic acid and mixtures thereof.

3. A diester of claim 2 wherein x and y each is 1.

v4. A diester of claim 2 wherein x is 2 and y is 0.

5. Diesters of (a) an aromatic dihydroxy carbonyl compound selected from the group consisting of 2,2'-dihydroxybenzophenone, 4,4'-dihydroxybenzophenone, 2,4-dihydroxybenzophenone, 2,4'-dihydroxybenzophenone, 2,2-dihydroxy-4,4-dimethoxybenzophenone, 2,2-dihydroxynaphthophenone and 2,2'-dihydroxybenzobiphenone, and

(b) a branched chain acid having a quaternary carbon atom selected from the group consisting of: 2,2-dimethylpentanoic acid, 3,3-dimethylpentanoic acid, 4,4-dimethylpentanoic acid, 4,4-dimethylhexanoic acid, 3,3,4-trirnethylpentanoic acid, 4,4,5-trimethylhexanoic acid 3,3-dimethylbutanoic acid, 2-methyl-2-ethylpentanoic acid, 3-methyl-3-ethylpentanoic acid, 3-methy1-3-ethylbutanoic acid and mixtures thereof.

6. A diester of claim 9 wherein the aromatic dihydroxy carbonyl compound is 2,4-dihydroxybenzophenone and the branched chain acid having a quaternary carbon atom is selected from the group consisting of 2,2-dimethylpentanoic acid and 3,3-dimethylpentanoic acid and mixtures thereof.

7. A diester of claim 2 wherein the aromatic dihydroxy carbonyl compound is 2,2'-dihydroxybenzophenone and the branched chain acid having a quaternary carbon atom is 2,2-dimethy1pentanoic acid.

8. A diester of claim 2 wherein the aromatic dihydroxy FOREIGN PATENTS carbonyl compound is 4,4-dihydroxybenzophenone and the branched chain acid having a quaternary carbon atom 636429 4/1950 Great,Br.1ta.m 26O 479 is zgzdimethylpentanoic acid 855,242 11/ 1960 Great Bntam 260-479 5 References Cited JAMES A. PA'ITEN, Pnmary Exarmner UNITED STATES PATENTS 3,024,270 3/ 1962 Havens et a1 260-45.85

3,072,602 1/1963 Clark et al 260-45.85 10 252-57; 26029.1 R, 408, 410.5, 544 Y 3,462,468 8/1969 Taylor et al. 260-479 *zg g g UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,632,630 Dated n y 4, 1972 Inventor(s) 'Iai S. Chao and Manley Kjonaas It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 66, delete "9"'and insert in place thereof Signed and sealed this 30th day of May 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

